This invention relates to dot printers in which dot printing is carried out using printing hammers, for example those disclosed in U.S. Pat. No. 3,941,051 or printing wires, for example as disclosed in U.S. Pat. No. 3,999,644, and more particularly to a mechanism which reciprocates a hammer bank incorporating such printing hammers or printing wires and drive means therefor along a printing line.
In the case of a printer in which the printing hammers or wires are driven while such a hammer bank is reciprocated along a printing line, the weight of the hammer bank is considerably large and the speed of movement of the hammer bank is high. Accordingly, the printer itself is greatly vibrated. In order to decrease printer vibration, a method has been employed in which the hammer bank and a counterweight having a weight equal to the weight of the hammer bank are reciprocated in opposite directions.
The hammer bank and the counterweight are provided on both sides of an elliptic cam. The hammer bank and the counterweight are each moved by the cam in one direction and by a spring in the opposite direction. Accordingly, the drive source such as an electric motor must have a large capacity, because it must move both the hammer bank and the counterweight against the elastic force of the springs. This tendency is increased as the speed of the hammer bank, i.e., the speed of rotation of the cam, is increased to increase the printing speed. If a large capacity drive motor of large size is employed as the drive source, problems as to installation space and cooling means arise, and it becomes impossible to miniaturize the printer.